In general, the present invention relates to switching power supplies. In particular, the present invention is directed to a self-supplied DC/DC switching power supply that is fully operational with a minimum input voltage and thereby provides improved regulation and efficiency within a wide range of input voltages.
Notification of an emergency is critical in a number of industrial applications, including but not limited to hospitals, military installations, traffic control installations, weather monitoring systems, manufacturing processes, nuclear facilities, large banking facilities and elevators. Computers and data processing equipment that enable such systems to operate often implement essential circuitry to provide visual or audio indicia (i.e., lighting, sirens or the like) that direct personnel to safety in the event of a threat to human life or property.
Circuitry of this type often includes a switching power supply (SPS) circuit. SPS circuits have certain properties that make them desirable. For instance, there is very little power dissipation, making switching supplies very efficient even if there is a large drop from input to output. Switching power supplies can also generate output voltages that exceed the input voltage such that they can run directly from a rectified power line with no AC power transformer. The result is a compact, lightweight and efficient power supply that is desirable for universal use in computers and computer-aided devices.
Since many electrical devices (including emergency notification devices) typically require DC power, a particularly useful type of SPS circuit is a DC/DC converter. Building power is typically 120 volts AC or greater, requiring a power supply to obtain the DC voltage necessary to operate such devices. DC/DC converters are highly efficient and economical devices that convert a DC voltage from a source such as a battery into a high DC voltage that can energize LEDs, lamps, buzzers and similar emergency notification devices. Typically the output produced is at a different voltage level than the input, however, some converters have the same input and output and are used to provide noise isolation, power bus regulation and similar functions.
In a conventional DC/DC converter as illustrated in FIG. 1, a switching power supply (SPS) circuit 1 includes input terminal 3 having an input voltage Vin applied thereto by an external DC power source (not shown). Input terminal 3 is electrically connected to a control circuit 5 that drives a switching element 7 such as a transistor. Input terminal 3 is further connected to one end of an inductor 9 that is in series with each of switching element 7, control circuit 5 and a rectifying filter 11. Rectifying filter 11 includes diode 13 having an anode in electrical communication with each of inductor 9 and switching element 7 and a cathode in electrical communication with each of capacitor 15 and output terminal 17, at which a power supply output voltage Vout is realized.
In operation, an external DC power supply applies an input voltage Vin to circuit 1 at input terminal 3 such that a current instantly flows in a path from input terminal 3 to control circuit 5 and inductor 9. Almost immediately after input voltage Vin is applied, such input voltage activates control circuit 5 and is subsequently applied to switching element 7. Switching element 7 periodically applies the full input voltage across inductor 9 for short intervals such that energy is stored in its magnetic field. The stored energy is transferred to filter 11 for rectification of the AC voltage by diode 13 and smoothing of the rectified DC voltage by capacitor 15.
In an SPS circuit of this type, the input voltage supplies the control circuit, thereby limiting the range of input voltages to a minimum value required to maintain operation of the control circuit. Reduction of the input voltage thus requires corresponding reduction of the lowest requisite voltage necessary to operate the control circuit. Because the lowest possible operation voltage of the elements (i.e. MOS transistors) constituting the control circuit is so restricted, the lowest achievable operation voltage for the SPS circuit is likewise limited. Such a restriction not only inhibits operation of the circuit below certain voltage thresholds. Existing designs that require a minimum input voltage (typically at least 0.75 V DC) also mandate the incorporation of expensive, sophisticated technologies like CMOS integrated circuits for reliable execution of SPS functions. The components comprising such technologies complicate such circuits, incurring additional costs associated with the acquisition, operation and maintenance thereof.
It is therefore desirable to provide a DC/DC converter that remains operative using a low input voltage source such as a low voltage battery pile. Such a converter would obviate the limitations on the circuit""s operation that are currently imposed by the operation voltage requirements of a control circuit incorporated therewith.
It is an advantage of the present invention to provide a self-supplied DC/DC switching power supply circuit.
It is another advantage of the invention to provide a DC/DC switching power supply circuit having a control circuit supplied by two alternate sources.
It is yet another advantage of the present invention to provide a regulated output DC voltage source having small size and which is relatively inexpensive to produce.
It is still another advantage of the present invention to remove the limitation of input voltage values on the threshold required for activation of a control circuit and subsequent functionality of a switching power supply circuit within which the control circuit is implemented.
In the pursuit of these and other advantages, the present invention provides a self-supplied DC/DC switching power supply (SPS) circuit for emergency notification and similar applications. The circuit includes a control circuit in electrical communication with an igniter circuit. The igniter circuit provides a temporary activation voltage to the control circuit for activation thereof. The igniter circuit provides the activation voltage for a limited time duration sufficient for enablement of the SPS circuit after which time power is supplied to such control circuit by the output voltage. The present invention SPS circuit can use a single-cell battery pile or other low-voltage sources as low as 0.3VDC while realizing improved efficiency of the circuit over a wide range of input voltages.